The present invention relates to a labeling device in a labeling machine with the continuous introduction of a film containing labels in reel form.
In particular the device in question is used mainly for the application of labels obtained by cutting a thin film of polypropylene or PVC or plastic film in general on which the images and data forming the label are printed. However, it could also be used for a film of other material, for example of the paper type.
The labeling devices which use films containing labels comprise: a group unwinding the film supplied from the reel; a cutting group consisting of a vertical blade mounted on a roller rotating about a vertical axis and a fixed vertical counterblade; a drum for picking up and transferring the cut label towards a roller for spreading the glue in predetermined zones and subsequently onto the container. Both the roller carrying the blade and the pickup drum are provided with internal chambers inside which a vacuum is created, and the chambers communicate by means of a plurality of holes with the external surface of the roller or the drum so as to suck up and retain the labels during the stage of cutting and transfer onto the drum and so as to keep them on the drum itself. The transfer drum is provided with a plurality of buffer pads which project from the external surface of the drum itself and which have the function of causing the label to adhere to the roller spreading the hot glue only in the region of said buffer pads so as to spread the glue only in predetermined zones of the label, in general on the leading edge and the end edge of the label, said edges being superimposed so as to be joined together when wound around the container.
Cutting of the film which in some cases as a thickness of a few hundreths of a millimeter poses various problems due mainly to bending or deformation of the movable blade support and the fixed blade or counterblade support. In the devices of the known type, the deformation occurs mainly for two reasons: owing to non-uniform thermal expansion throughout the rotating roller; on account of the blade fixing systems which fix the blade to the external surface of the roller itself.
Another drawback is due to the fact that the distance of the blades with respect to the drum for picking up and transferring the cut label is considerable and this necessitates the use of special grippers for gripping the label, which are housed on the drum also provided with holes through which a suction effect is created, said suction effect being designed to retain the label along the whole of its transfer path. The considerable distance between counterblade and pickup drum often results in the inexact positioning of the label on the drum with consequent positioning of the layer of glue in the wrong position. Moreover, the label may be positioned in a crooked manner on the container, resulting in rejects. On account of the considerable space between the cutting point and the gripping point, the label remains free during a part of its path where it may become inclined and hence be positioned on the drum incorrectly. This drawback represents more of a problem in the case of short-length labels for small containers.